What’s the handle of a combat knife made out of? I Googled it and it said polymer. Would it be more plastic or steel?
All plastics are polymers; not all polymers are plastics. While there are a lot of variations, modern combat knives will (usually) have a polymer grip. In most cases, that will be a rubberized polymer, meaning it has some give and traction when held. (Worth knowing, rubber, including natural rubber, is a polymer. Rubber is not a plastic. Most synthetic rubber is not a plastic.)
With higher end modern knives, you can probably replace the grips, meaning you can choose between a harder, ridged, “plastic-like,” grip, or a softer, rubberized grip. (You can also get rubberized grip attachments for some firearms.
Older combat knives from the last century were more likely to feature wooden grips. Some modern knives may support a wooden grip, if you’re so inclined. Wooden grips will still pop up as luxury options, or on some hunting knives.
While it’s more of a luxury item, Ivory grips are quite popular in some circles. Real ivory is expensive, and regulated, but synthetic ivory is much cheaper. In this case, the grip may be hand carved.
Certainly not common, but there is still application for shagreen (shark and ray skin) and leather grips. In particular, you can obtain ray shagreen fairly easily. This isn’t likely to be the standard grip, but certainly could be something that an individual may want to use. Shagreen is noteworthy because it remains easy to grip in adverse weather (such as in heavy rain.) Shagreen used to be the norm for naval sword grips (in the 19th century.)
A lot of these latter examples would be non-standard modifications, but you may encounter them.
Metal grips are far less attractive, but you will frequently find them on collapsible blades. Also, a lot of the above examples will have a metal core, with the grips above attached to it. The biggest flaw for a metal grip is that it will become slick when wet. Understandably, when you start poking holes in someone, your blade and grip are prone to becoming a bit wet.
But, yeah, the answer you found was correct, polymer grips are going to be the most common.
This blog is supported through Patreon. If you enjoy our content, please consider becoming a Patron. Every contribution helps keep us online, and writing. If you already are a Patron, thank you, and come join us on Discord.